1. Field of the Invention
The present invention relates in general to the field of fiber optic communications, and particularly to the aspects related to the deployment of cablings for the connection of user devices to optical networks.
2. Discussion of the Related Art
The deployment of broadband communications networks also calls for using optical fibers for the so-called “last mile”, i.e. the last trunk of the communications network to which the user devices, like for instance modems, set-top boxes for receiving cable television services, IP (Internet Protocol) phones and similar devices, are directly connected.
Typically, the deployment of the last mile of an optical network provides for posing in the field optical cables containing a plurality of optical fibers, for instance in a number variable from 6 to 48; the cables are routed through conduits that can for example develop through or along the walls of a multi-floor building, often for more or less vertical segments, or, in the case of residential zones with houses set in succession along a city street, the optical cables extend horizontally through conduits preferably located under of the ground level.
Typically, an optical cable of the type adapted for this use includes a tubular element, or sheath, inside which several optical fibers are placed. Depending on the specific type of application, the optical fibers can be accommodated within the sheath without protections, or they may be covered by a protective coating, or they may also be gathered in independent groups (also referred to as microcables or micromodules) contained in a thin tubular coating. In the following, where not otherwise specified, such combinations of optical fibers are defined as “optical fiber units”.
In order to make the connection of the different user devices to the optical network possible, it is necessary to lead one or more optical fibers to the sites (apartments, houses, offices) of the users. To this end, openings need to be to made in the sheaths of the optical cables, so as to be able to access the optical fibers accommodated within each cable; through such openings, the optical fibers can be at least partially drawn out, extracted from the cable and routed to where needed, for example to sockets provided for in the premises of the users, to which the respective devices can be connected.
A similar cabling method is described, for instance, in the International application No. WO 2006/136558, according to which in the sheath of an optical cable containing several optical microcables two openings are made, a first opening in correspondence of the point at which the cabling for the connection of a subscriber has to be realized, and a second opening downstream thereof, at a distance of the order of about some meters or tens of meters from the first opening; one of the optical microcables contained in the optical cable is selected (for example based on its color) and cut in correspondence of the second opening, and the segment of microcable between the first opening and the point of cut is then extracted from the optical cable through the first opening. The extracted microcable segment is then inserted into a pre-installed microconduit that extends to the connection point of the subscriber, or, depending on the circumstance, to a branch box.
It often happens that the optical cable has to be passed through conduits already existing in the buildings, originally intended to contain other types of cables, for instance for the distribution of electric energy and/or of television and/or telephone signals, and that the extraction from the cable of the optical fibers for the connection to the different user devices has to be made in correspondence of already present branch boxes. This is for example the case where optical fibers have to be deployed in buildings built in relatively remote times. The branch boxes, serving for a plurality of purposes, are in such cases accessible to technical personnel of disparate nature, for instance operators of the electric energy distribution network or of the telephone company, or people entrusted with the maintenance of the building, and this constitutes a risk factor for the integrity of the optical fibers, which, as known, are relatively delicate structures, and their manipulation should be allowed only to specialized personnel. Additionally, the branch boxes can result particularly crowded with cables of disparate nature. Pressures and undue crushing of the optical fibers in consequence of the access to the branch box, particularly made even more likely by the non-careful behavior of technicians that are not accustomed to handling optical fibers, can cause damages to the optical cable, particularly to the optical fibers extracted therefrom for the connection of the users, as well as of the optical fibers that remain partially exposed in correspondence of the openings made in the cable for the extraction of the fibers.
In the International application No. WO 2008/008115 the use is described of a transition tube in flexible material for the protection of an optical fiber extracted from an optical cable through an access location, as well as the use of a cap to close again the access location and to protect the remaining fibers present in the cable. After having extracted the fiber from the optical cable, the transition tube is inserted thereon, up to partially push it within the same optical cable; the cap is then placed to close the access location, and the cap is attached in a non-removable way to the optical cable through adhesive or similar. After having made the junction (“splice”) of the fiber extracted from the cable to a section of connection fiber (also referred to as “pigtail”), a sleeve in thermo-retractable material is finally put on the optical cable that seals both the zone of extraction of the optical fiber from the cable, and the zone of junction (“splice”) between the fibers.
Such operation, that involves head-to-head splicing of the fibers, is performed in factory, in a controlled environment.